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2,735,048 POWER TRANSMISSION DEVICE Monroe D. Levy, University City,Mo., assignor to Vickers Incorporated, Detroit, Mich., a corporation ofMichigan No Drawing. Application March 15, 1951, Serial No. 215,867

14 Claims. (Cl. 317-234) This invention relates to power transmissionand more particularly to blocking layer devices such as seleniumrectifier and light-sensitive cells, and to methods of making suchdevices.

num, etc.; (2) the selenium layer is heat-treated to change it from theamorphous state to its conducting crystalline form; (3) an artificialbarrier layer, such race of the counterelectrode and the selenium layer,due to a barrier at that point. not known with any degree of manyartificial These are generally formed by treating the annealed have beenemployed with varying degrees of success in improving the rectificationratio of rectifier cells.

The present invention has special utility in the manuratio in the endproduct. After the baking step the unit is electroformed in the usualmanner.

It is therefore an object of the invention to provide a nited StatesPatent method of forming an artificial barrier layer in a blocking layerdevice.

Another object of the invention is to provide a method of making ablocking layer device with improved rectification characteristics.

Still another object of the invention is to provide a blocking layerdevice having improved electrical characteristics.

Further objects and advantages of the present invention will be apparentfrom the following description.

2,735,048 Patented Feb. 14, 1956 preferred, such as low boiling pointalcohols, low boiling point ketones, etc. Examples of such solvents aremethyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, and ethylmethyl ketones. Water may be used as a solvent with a sacrifice in theuniformity of the applied coating because of low wetting ability.

Although the selenium coated plates may be clipped in the solution,spraying permits a better control of the concentration per unit area.The actual amount of the rectification ratio is improved with anyincrease in concentration. However, too great a concentration willresult in an impractical low forward conductivity even though theresulting rectification ratio in itself will be high.

hydroxide concentrate in the solvents.

In general, concentrations on a volume basis of about one part of thehydroxide in 50 to 1000 parts of solvent provides a wide variety ofconcentrations from which a suitable choice selected method ofapplication.

With the fast drying solvent the sprayed solution dries RN*-0H N is thenitrogen atom, OH is the hydroxyl radiwhere cal, and each R 15 a radicalor group having three carbon atoms or less, for example, tetraethanolammonium hydroxide whose formula is is intended to cover not only thecase where each R is the same, but also where the radicals are mixed,for example, dimethyl diethyl ammonium hydroxide CH2. (31K:

Gs CzHi It is apparent that each R is a radical having three carbonatoms or less.

After the hydroxide application is dry, 2. suitable counterelectrode isplaced on the treated selenium surface; For instance, thecounterelectrode may be formed by spraying onto the treated seleniumsurface a low melt ing metal or alloy. There are many known alloysusable as counterelectrodes and the process herein is not confined tothe use of any particular counterelectrode material. Examples ofcommonly used alloys which were used in the practice of the methodherein are: 70% tin- 30% cadmium; 20% tin-80% cadmium; and the 130eutectic alloy of tin, bismuth, and cadmium.

After the counterelectrode is applied the composite unit is heated byany suitable means such as baking in an oven. The heating temperature ispreferably below the melting point of the electrodes, and thetemperature and the length of heating time may be varied depending uponthe final cell characteristics desired.

Although the temperature and time of heating or baking is not critical,the most practical ranges extend from about 50 C. to about 150 C., andfrom about ten minutes to about six hours. The lower the temperature,the more time is required to achieve a particular end characteristic.Tests show that for a selected temperature the end characteristic willvary with the heating time. In a test of a series of cells madeaccording to the method herein and where the melting point of thecounter- 3 electrode was 103, a baking temperature of 95 was selected,and the following results were tabulated after the cells wereelectroformed.

The following tables show examples of cell groups treated by sprayingthe crystalline layers with tetraethanol ammonium hydroxide inintermediate concentrations by volume of one part hydroxide in 250, 500,and 750 parts methyl alcohol, respectively.

Concentration 1 part in 750 lmkinflf Av. Voltage B t a g ec No. of CellsO" Ratio minutes Inverse Forward SAME CELLS AFTER 1 WEEK SHELF AGINGConcentration 1 part in too Biggie o! Av. Voltage R t mg on No. of Cells0 O Ratio minutes Inverse Forward Concentration 1 part m :50

Time of Av. Voltage Y Baking Rect. l\0. of Cells 0" Ratio minutesInverse Forward SAME CELLS AFTER 1 WEEK SHELF AGING The above chartsindicate that higher concentrations decrease the reverse conductivityand that cell stability is enhanced by a longer heating time. The chartsalso indicate that with a longer baking time, shelf aging afterelectroformation tends to further improve the rectification ratio. It ispreferable to stabilize the plates by aging them after electroformation,regardless of the baking time employed.

Improvements of at least 24% in the rectification ratio of the endproduct have been obtained by the addition of the baking step. After thebaking step, the composite unit is electroformed by any suitable method,such as applying unidirectional current to the cell in the reversedirection until the desired rectification ratio is attained.

The term baking as used throughout the specification and claims isintended to cover all forms of heating.

While the form of embodiment of the invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted, all coming within the scope of the claims whichfollow.

What is claimed is as follows:

1. A method of forming a barrier layer in a selenium blocking layer cellwhich comprises surface treating a crystalline selenium layer with aquaternary ammonium hydroxide, applying a counterelectrode to thetreated selenium surface, baking the composite .cell before anyelectroforming, and electroforrning the cell, and quaternary ammoniumhydroxide having the general formula N+-OH- R R 1 where each R is agroup having less than four carbon atoms.

2. The method of producing blocking layer devices which comprisesproviding a supporting base with a layer of crystalline selenium,applying a quaternary ammonium hydroxide to the surface of the selenium,applying a counterelectrode to the treated selenium surface, and bakingthe composite product, said quaternary ammonium hydroxide having thegeneral formula n R +-0H- where each R is a group having less than fourcarbon atoms. i

3. A method of making blocking layer devices having a crystallineselenium layer ona base which comprises the steps of applying to thecrystalline selenium surface a solution of a quaternary ammoniumhydroxide in a solvent, applying a counterelectrode to the treatedselenium surface, baking the composite product before anyelectroforming, and electroforming the device said quaternary ammoniumhydroxide having the general formula N\'0K' B B r where each R is agroup having less than four carbon atoms.

of solvent, said quaternary the general formula \NQOH where each R is agroup having less than four carbon atoms.

for forming a barrier layer in a selenium device which comprises surfacetreating baking the composite product, said quaternary ammonium thegeneral formula where each R is a atoms.

6. A method for forming a barrier layer in a selenium blocking layerdevice which comprises surface treating group having less than fourcarbon where each R is a group having less than four carbon atoms.

7. A method of making blocking layer devices layer on a base whichcomprises hydroxide in a solvent, applying a counterelectrode to thetreated selenium surface, and baking the composite product, theconcentration range of the tetraethanol amwhere each R is 21 atoms.

12. A blocking layer device comprising a conductive base, a layer ofcrystalline group having less than four carbon R R where each R is agroup having less than four carbon atoms.

13. A blocking layer device comprising a conductive base, a layer ofcrystalline selenium unit before any electroforming.

14. A blocking layer device comprising a conductive base, a layer ofcrystalline

11. A BLOCKING LAYER DEVICE COMPRISING A CRYSTALLINE SELENIUM LAYER, ACOUNTERELECTRODE ON SAID LAYER, AND A BARRIER LAYER BETWEEN THEELECTRODE AND THE SELENIUM LAYER, SAID BARRIER BEING THE PRODUCT BY THEINTERPOSITION OF A QUATERNARY AMMONIUM HYDROXIDE BETWEEN THE ELECTRODEAND THE SELENIUM SURFACE AND BAKING THE COMPOSITE UNIT BEFORE ANYELECTROFORMING, SAID QUATERNARY AMMONIUM HYDROXIDE HAVING THE GENERALFORMULA